Bath for the electrodeposition of birght tin-cobalt alloy

ABSTRACT

A bright electroplated tin-cobalt alloy is obtained with an aqueous pyrophosphate electroplating bath which contains a brightening agent selected from the group which consists of amino carboxylic acid with sulphur, neutral amino acid, basic amino acid, peptone, protein, organo-sulphur compound, ammonia, ammonium salt, amine, and mixtures thereof.

United States Patent [191 Fueki et al.

[111' 3,914,160 [4 1 Oct. 21, 1975 BATH FOR THE ELECTRODEPOSITION OF BRIGHT TIN-COBALT ALLOY [75] Inventors: Shimetomo Fueki, Tokyo; Junichi Tada,'Yokohama; Kenji Osawa, Hino; Naomi Sakai; Kazuhiro Ogawa, both of Yokohama, all of Japan [73] Assignee: Sony Corporation, Tokyo, Japan [22] Filed: May 15, 1973 [21] Appl. No.: 360,542

[30] Foreign Application Priority Data May 17, 1972 Japan 47-48181 May 17, 1972 Japan 47-48182 May 17, 1972 Japan 47-48183 May 17, 1972 Japan 47-48184 [52] US. Cl. 204/43 S [51] Int. C1. CZSD 3/60 [58] Field of Search 204/43 S, 43 T Primary Examiner--G. L. Kaplan Attorney, Agent, or FirmLewis H. Eslinger; Alvin Sinderbrand [57] ABSTRACT A bright electroplated tin-cobalt alloy is obtained with an aqueous pyrophosphate electroplating bath which contains a brightening agent selected from the group which consists of amino carboxylic acid with sulphur, neutral amino acid, basic amino acid, peptone, protein, organo-sulphur compound, ammonia, ammonium salt, amine, and mixtures thereof.

8 Claims, No Drawings BATH FOR THE ELECTRODEPOSITION OF BRIGHT TIN-COBALT ALLOY BACKGROUND OF THE INVENTION 1. Field Of the Invention The present invention relates generally to a bright tin-cobalt plating bath and more particularly to a bright tin-cobalt plating bath with an additive as a brightener.

2. Description of the Prior Art In general, electroplated coatings of tin alloys have superior anti'corrosive characteristics. Tin-nickel alloy plating is one of the tin alloys that has been used and is superior in its anti-corrosive characteristic to a plating of tin or nickel alone. The tin-nickel alloy plating shows a reddish appearance. In order to carry out the tin-nickel alloy plating, an acidic fluoride bath is generally used, and the electroplated layer thus formed is very brittle and a crack is apt to be formed in the layer when stress is applied to it.

A pyrophosphate bath has been also proposed for the tin-nickel alloy plating, but the thus formed electroplated layer is also brittle and it is more difficult to control the pyrophosphate bath than it is to control the acidic fluoride bath. For this reason, the pyrophosphate bath is not used in practice.

Tin-cobalt alloy plating is also known to avoid the undesirable brittleness of the tin-nickel alloy plating. The tin-cobalt alloy plating is substantially equal to the tinnickel alloy plating in its anti-corrosive characteristic but is substantially better in its brittleness. In addition, cracks are not apt to form in the tin-cobalt alloy plating. .As a practical plating bath, an acidic fluoride bath is used and the thus formed plating has a color equal to that of chromium plating. Therefore, the tin-cobalt alloy plating may be employed as a finishing plating in place of the chromium plating which is usually employed.

However, the tin-cobalt alloy plating bath including fluoride requires difficult drainage and exhaust treatments so that such a bath is undesirable from the point of view of environmental pollution. I

A report (Electrodeposition of Alloys, Vol. '2, Academic Press, New York and London, P. 339 341, 1963 edited by A. Brenner) has been issued by V. Sree and T. L. Rama Char on tin-cobalt alloy plating from a pyrophosphate bath. The inventors ofthe present invention have carried out a test based upon such report and in which ammonium citrate is added to the pyrophosphate bath as an additive, as disclosed in the report. Throughout this test, the contents of the bath were agitated to carry out a so-called Hull Cell Test. The electroplated coating formed by this test had black or grey blurs.

SUMMARY OF-TI-IE INVENTION It is an object of the present invention to provide a bath for electrodeposition of bright tin-cobalt alloy which can produce a white bright tin-cobalt plating layer without the use of fluoride.

It is another object of the present invention to provide a brightener additive for an electrolyte consisting of stannous salt, cobalt salt and alkaline metal pyrophosphate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with the present invention, the brightener additive is an amino carboxylicjacid with sulphur either alone or together with ammonia, an ammonium salt or an amine compound; or glue, gelatin and/or peptone, a neutral or basic amino acid, or an organo sulphur compound which, in each case, is used together with ammonia, an ammonium salt or an amine compound.

In an alloy plating bath including tin, cobalt and pyrophosphoric acid, tin pyrophosphate may be easily dissolved into an aqueous solution of potassium pyrophosphate, but cobalt pyrophosphate is hardly dissolved into the aqueous solution of potassium pyrophosphate diluted by 1-20 times at atemperature of 60-80C.

An electroplating bath according to the present invention is formed as follows:

15 weight parts of potassium pyrophosphate are prepared for 1 weight part of cobalt metal; 40% aqueous cobalt salt solution is poured into potassium pyrophosphate water solution at about 60C with agitation to be dissolved therein; and thereafter aqueous stannous pyrophosphate solution is poured into the thus prepared.

aqueous solution with agitation to be dissolved therein. The complex salt of the resulting alloy plating electrolyte is high in stability so that with the addition of the brightener, as hereinafter 'dscribed in detail, abright tin-cobalt alloy plating is obtained merely with mechanical agitation and without accompanying any void electrolyzing. I

The cobalt salt is preferably selected from cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt bromide,

cobalt carbonate, cobalt acetate, ethylene diamine tetraacetic acid cobalt, cobalt (II) acetyl acetonate, cobalt (III) acetyl acetonate, glycine cobalt (III), and cobalt pyrophosphate.

The components of the electroplating bath according to the present invention are employed within the fol-' I lowing concentration ranges: The stannous salt is present in the aqueous solution in an amount to provide 2 to grams of stannous metal per liter of the aqueous solution; the cobalt salt is present in an amount to provide 1 to 40 grams of cobalt metal per liter of the aqueous solution, with the total concentration of the stannous and cobalt metals being less than grams per liter of the aqueous solution; and the amount of alkali metal pyrophosphate is sufficient to provide more than 2 mols thereof for each mol of the total concentration of stannous and cobalt'metals.

The amino carboxylic acids with sulphur. that may be used as the brightener additive in the plating electrolyte of the present invention are preferably selected from the group of cysteine, methionine, cystine, homocystine, homocysteine, ethionine, and cystine disulfoxide. The necessary amount of these compounds is 0.01-5 g/l. If the amount of these compounds is less than 0.01 g/l, the brightening effect is not obtained and if the amount is is higher than 5 g/l, no increase is ascertained in the brightening effect.

The amino acids that may be added to the plating electrolyte of the present invention are neutral or basic amino acids, preferably from the group of amino acids comprised of glycine, alanine, valine, leucine, norleucine, isoleucine, phenylalanine, serine', threonine, tryptophan, tryosine, thyroxine, lysine, arginine, and histidine. The amount of these amino acids to be added to the plating bath is 0.1- g/l.

The protein and/or peptone that may be added to the plating electrolyte of the invention as a brightener, are preferably from the group comprised of glue, gelatin, peptone and gluten, and their necessary amount is 0.1-80 g/l. The additive compounds are added to the bath after being dissolved into water, caustic alkali, water solution of potassium pyrophosphate or into alcohols, such as methanol, ethanol and the like.

Among the organosulphur compounds which may added to the plating electrolyte of the invention are dithioammelide, 4-amino-3,5-dimercapto-4,l,Z-triazole ethylene thiuram monosulfide, 2.5-dimercapto-l,3,4- thiadiazole thiocarbohydrazide, hydrazodithiodicarin contact. Further, even if a brine solution is sprayed against the plated layer formed by the invention for about 72 hours, no changes occur. When the test piece having the plated layer thereon according to this inven- 5 tion is repeatedly bent up and down by about 90 through a tester with 4mm bending radius, the plated layer is not peeled off the test piece or powdered. The hardness of the plating is on the order of 500 on the Vickers hardness scale.

EXAMPLES 1,2

bonamide, ethylene-bis-dithio-carbamic acid sodium I Examplcz salt and the like, in a concentration of 0.01-5 g/l.

The ammonia, ammonium salts and amine com- Pmflssium PY P P B 250 250 pounds which may be added to the plating electrolyte i'fj fi ffl 'ff jff g: of the invention, are preferably from the group combaitacetale g/l 30 prised of water solution of ammonia, ammonium chlogit lg 5. 5 3 ride, ammonium citrate, ammonium tartrate, ammopH 10.0 nium sulfate, ammonium acetate, ethylenediamine, cathode rocker exist 1,2-propaned1am1ne, 1,3-propaned1amme, 1,4- current density A/dm2 I butanediamine, hydroxylamine hydrochloride, hydramount of Contained educed tin 80.5 8l 5 zine, methylamine, ethylamine, propylamine, butyla- Appearance mine, piperazine, pyrrolidine, monoethanolamine, di- Anode carbon ethanolamine, and triethanolamine. The necessary amount of 28% aqueous solution of ammonia is 201OO cc/l and the necessary amount of the ammonium salts and amines compounds is 0.1-150 g/l.

EXAMPLES 3 to 10, and Reference Example Reference 3 4 5 6 7 8 9 l0 potassium pyrophosgll 250 25 0 250 250 250 250 250 250 -250 phate tin pyrophosphate gll l5 l5 l5 l5 l5 l5 i5 15 I5 cobalt chloride g/l 30 30 30 30 30 cobalt sulfate g/l cobalt acetate g/l 30 30 water solution of ammonia 28% cell 70 2O 30 70 1,3-propanediamine cell 3 3 3 l triethanolamine cell 1 glycine gll I0 10 5 5 alanine gll 20 phenyl-alanine g/l I methionine g/l 2 2 lysine g/l l 2 PH on n H H H H I, l, I, temperature cc n I, I, H H H H n cathode rocker exist current density A/dm? O.5-2 i amount of contained 80.3 80.6 80.9 79.9 81.2 80.5 81.5 86.0 85.8

educed tin Appearance white bright Anode carbon I. l, H u H u H I,

The plating bath according to the present invention is 8.0l 2.0 in pH, 20-70C in temperature and 0.1-4.0 A/dm in current density. The plating with the plating V In the above table, the mark means that the appearance of the plating is not white but it has dark grey blurs and hence it can not be used practically.

bath of the invention is found to be effective when sub- 55 It will be apparent from the above Examples and the jected to mechanical agitation, cathode rocking or a combination thereof.

The bright tin-cobalt alloy plating formed by the plating bath of the present invention has an appearance Reference that the bright tin-cobalt alloy plating formed in the pyrophosphate bath is obtained by the addition, as a brightener to such bath, of amino carboxylic acid with sulphur itself or the combination of (1) imilar t that Of Chromium plat ng and is superior in at least one member of the group consisting of neutral anti-corrosive characteristic, so that even ifit has been exposed to atmosphere for about thirty days no color change occurs and corrosion does not appear at the' portions thereof with which human fingers have been amino acids and basic amino acids, with (2) at least one member of the group consisting of ammonia, ammonium salts and amine compounds.

EXAMPLES 11-17 Example I 1 l2 l3 l4 l5 l6 l7 potassium pyrophosgll 250 250 250 250 250 250 250 phate tin pyrophosphate g/l 15 15 l5 l5 l5 l5 l5 'Cont1nued Example l l l2- l3 l4 l5 l6 l7 cobalt chloride g/l 30 I 30 30 30 30 cobalt sulfate g/l 35 1 cobalt acetate g/l 30 water solution of ammonia 28% cell 70 70 7O l,3-propancdiaminc cc/l 3 3 1 glue 3/! l gelatin g/l 1 1 1 1 4 1 peptone g/l l 20 l0.0 Temperature C 55 cathode rocker exist current density A/dm 0.5-2 Y amount of contained 80.5 80.3 81.4 80.8 80.5 80.3 S l .l educed tin Appearance white bright Anode carbon It will be apparent from the above Examples 1 l to 17 that the bright tin-cobalt alloy plating formed in the py- 4. Th'e'electroplating is very smooth at its marginal edge and even if the electroplating has thickness of TOPhOSPhate, as the addmve, bath is la y g 20 1-3 microns on a nonconductive material base with one or more of glue, gelatm and peptone, 1n combmaa relativgly l current d i f .1 t1on with ammonia or an amine compound. peres/dm the electroplating has high anti- EXAMPLES 18 to 24 corroslve charcter1st1cs and a fine appearance. The

Example l8 19 20 21 22 23 24 potassium pyrophosphate g/l 250 250 250 250 250 250 250 tin pyrophosphate g/l l5 l5 l5 l5 l5 l5 l5 cobalt chloride g/l 30 30 cobalt sulfate g/l 35 cobalt acetate g/l 30 30 water solution of ammonia 28% cell 70 1,3 pr0panediamine cc/l 3 3 3 triethanolamine cell 1 2 dithioammelide g/l 0.6 0.8 0.5 4-amino-3,5- dimercapto-4, g/l 0.8 l ,Z-triazole hydrazodithiodicarhonamide g/l 0.8 0.8 2 0.5 PH 100 1, 1, ,1 1. I, H Temperature C Cathode rocker exist current density A/dm 0.5-2 amount of contained 80.3 80.7 79.8 80.9 80.1 80.3 80.8 educed tin Appearance white bright Anode carbon 1, n 1, I, H .1

It will be apparent from the above Examples 18 to 24 that the bright tin-cobalt alloy plating formed in the pyrophosphate bath is obtained by using, as the additive, the combination of ammonia, an ammonium salt or an amine compound with an organosulphur compound,

other than an amino carboxylic acid with sulphur which, as previously indicated may be used alone as the additive according to this invention.

The advantages of the bright tin-cobalt plating electrolyte of the present invention are summarized as follows:

l. Drainage and exhaust treatments are easily achieved because fluoride is not used in the bath. 2. Electroplating is carried out at room temperature,

which is not the case when using fluoride which requires temperature of 6590C. Thus, electroplating according to the invention can be applied to plastics.

. If the electroplating has a thickness of more than 10 microns, it shows an appearance similar to that of chromium plating and it is superior in anticorrosive characteristic and not brittle. As a result, the electroplating can be used as both a finishing and a base plating.

electroplating is suited for those applications where chromium plating can not be employed.

5. The electroplating can be applied to electronic parts, acoustic devices, optical devices, precision apparatus, parts for automobiles and ornaments.

It will be apparent that many variations and changes may be effected without departing from the spirit and scope of the novel concepts of the present invention.

We claim as our invention:

1. A bright tin-cobalt alloy electroplating bath consisting essentially of an aqueous solution of:

a. a stannous salt present in an amount sufficient to provide from 2 to grams of stannous metal per liter of said solution;

b. a cobalt salt present in an amount sufficient to provide from 1 to 40 grams of cobalt metal per liter of said solution, with the total amount of said stannous and cobalt metals being less than grams per liter of said solution;

an alkali metal pyrophosphate present in an amount providing more than 2 mols thereof for each mol of said total amount of said stannous and cobalt metals; and d. at least brightener additive selected from the group consisting of amino carboxylic acids with sulphur and which is present in said solution in an amount I of from 0.01 to grams per liter of said solution.

2. A bright tin-cobalt alloy electroplating bath according to claim 1; in which said stannous salt is tin (ll) pyrophosphate.

3. A bright tin-cobalt alloy electroplating bath according to claim 1; in which said cobalt salt is selected from the group consisting of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt bromide, cobalt carbonate. cobalt acetate, ethylene-diamine tetraacetic acid cobalt, cobalt (ll) acetyl acetonate, cobalt (lll) acetyl acetonate, glycine cobalt (Ill) and cobalt pyrophosphate.

4. A bright tin-cobalt alloy electroplating bath according to claim 1; in which said alkali metal pyrophosphate is potassium pyrophosphate. 1

5. A bright tin-cobalt alloy electroplating bath according to claim 1-; in which said brightener additive is cystine.

6. A bright tin-cobalt alloy electroplating bath according to claim 1; in which said amino carboxylic acids with sulfur are the group consisting of cystine, methionine, cysteine, homocystine, homocysteine. ethionine and cystine disulfoxide.

7. A bright tin-cobalt alloy electroplating bath according to claim 1; in which said brightener additive is cysteine.

8. A bright tin-cobalt alloy electroplating bath ac-:

cording to claim 1; in which said stannous salt is tin pyrophosphate, said cobalt salt is cobalt sulfate, said alkali metal pyrophosphate is potassium pyrophosphate, and said brightener additive is methionine. 

1. A BRIGHT TIN-COBALT ALLOY ELECTROPLATING BATH CONSISTING ESSENTIALLY OF AN AQUEOUS SOLUTION OF: A. A STANNOUS SALT PRESENT IN AN AMOUNT SUFFICIENT TO PROVIDE FROM 2 TO 70 GRAMS OF STANNOUS METAL PER LITER OF SAID SOLUTION, B. A COBALT SALT PRESENT IN AN AMOUNT SUFFICIENT TO PROVIDE FROM 1 TO 40 GRAMS OF COBALT METAL PER LITER OF SAID SOLUTION, WITH THE TOTAL AMOUNT OF SAID STANNOUS AND COBALT METALS BEING LESS THAN 75 GRAMS PER LITER OF SAID SOLUTION, C. AN ALKALI METAL PYROPHOSPHATE PRESENT IN AN AMOUNT PROVIDING MORE THAN 2 MOLTS THEREOF FOR EACH MOL OF SAID TOTAL AMOUNT OF SAID STANNOUS AND COBALT METALS, AND D. AT LEAST BRIGHTENER ADDITIVE SELECTED FROM THE GROUP CONSISTING OF AMINO CARBOXYLIC ACIDS WITH SULPHUR AND WHICH IS PRESENT IN SAID SOLUTION IN AN AMOUNT OF FROM 0.01 TO 5 GRAMS PER LITER OF SAID SOLUTION.
 2. A bright tin-cobalt alloy electroplating bath according to claim 1; in which said stannous salt is tin (II) pyrophosphate.
 3. A bright tin-cobalt alloy electroplating bath according to claim 1; in which said cobalt salt is selected from the group consisting of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt bromide, cobalt carbonate, cobalt acetate, ethylene-diamine tetraacetic acid cobalt, cobalt (II) acetyl acetonate, cobalt (III) acetyl acetonate, glycine cobalt (III) and cobalt pyrophosphate.
 4. A bright tin-cobalt alloy electroplating bath according to claim 1; in which said alkali metal pyrophosphate is potassium pyrophosphate.
 5. A bright tin-cobalt alloy electroplating bath according to claim 1; in which said brightener additive is cystine.
 6. A bright tin-cobalt alloy electroplating bath according to claim 1; in which said amino carboxylic acids with sulfur are the group consisting of cystine, methionine, cysteine, homocystine, homocysteine, ethionine and cystine disulfoxide.
 7. A bright tin-cobalt alloy electroplating bath according to claim 1; in which said brightener additive is cysteine.
 8. A bright tin-cobalt alloy electroplating bath according to claim 1; in which said stannOus salt is tin pyrophosphate, said cobalt salt is cobalt sulfate, said alkali metal pyrophosphate is potassium pyrophosphate, and said brightener additive is methionine. 